Fixes route error when embeding slim

Setup:

Full website is on http://domain.tld/
Slim is installed on http://domain.tld/mobileApp/
Slim Public route is: http://domain.tld/mobileApp/public << but it's not used, keep reading.

-We detect if a cookie is set where we know if the user is on a mobile device
-.htaccess catches the cookie and rewrites the request to the "slim public route" (no redirection occurs as it needs to use the same domain)
-Slim fails to understand that the physical path is not there because its being called from somewhere else and the router fails.

this fix just checks if the $physicalPath is there before trying to remove it.